In conventional refrigeration systems, if pressure buildup within the system exceeds a predetermined value, a safety valve will open to release refrigerant to the atmosphere. This relieves pressures within the system and therefore avoids damage to the refrigeration system or an explosion which could cause property damage or injuries. A refrigeration system which employs a safety valve (23) which releases refrigerant to the atmosphere is disclosed in U.S. Pat. No. 1,703,299 to Copeman.
Conventional safety or relief valves are usually designed to vent overpressure in a system and then reseat when the system pressure returns to a value lower than the safety valve set point. Often, for various reasons such as age, infrequent use, contamination, or debris on the seat the safety valve does not properly reseat. This can cause the entire refrigerant charge to be vented from the system, which for large systems means a thousand pounds of refrigerant or more will be released to the atmosphere. Even when the safety valve properly reseats, a substantial portion of the refrigerant may be released to the atmosphere. Thus, in conventional systems, the potential for refrigerant release to the atmosphere exists regardless of whether the relief valve is operating properly.
Release of refrigerants to the atmosphere, while saving the equipment, unfortunately may contribute to pollution of the atmosphere. The U.S. and more than 80 other countries have reached a pact to halt the production of chlorofluorocarbons, or CFC's after 1995. The leading coolants slated for replacing CFC's in the next generation of industrial air conditioners, or chillers, are HFC 134a and HCFC 123. Even these CFC substitutes have been accused of exhibiting some global warming effect, or small ozone-depletion effect, or causing benign tumors in rats. CFC's may be used after the production deadline, but costs for the refrigerants will greatly increase as the supply decreases. CFC's have already increased from less than one dollar a pound ten years ago to over $7.00 per pound. It is estimated that the pool of CFC's after the ban on production will supply only about 25% of current needs.
Thus, there exists a great need for conserving refrigerant, whether it be the banned CFC's or their proposed replacements, both from an ecological view and from an economic one.
European patent no. 250,914 employs a valve 8 and a container 1 downstream of the valve to collect refrigerant and prevent the refrigerant from being released to the atmosphere during refrigerant draining.
Japanese patent no. 28,967 discloses an expansion tank 11 which communicates with the high pressure side of the refrigerant system via line 17. The tank is connected to the inlet of a compressor by a capillary tube 14 and a check valve 15. A valve is opened when a discharge pressure of the compressor exceeds a specified value. The valve actuator 13 is controlled by element 12 which in turn communicates with the discharge of the compressor 1.
U.S. Pat. No. 5,186,017 to Hancock et al employs tanks 16 (FIGS. 1 and 2) and 316 (FIGS. 6 to 8) to accept refrigerant from the high pressure side of the refrigerant system. Condition responsive controlled compressors 172 (FIG. 2) and 372 (FIGS. 6 to 8) return vapor from the tank to the refrigerant system.
U.S. Pat. No. 3,736,763 to Garland illustrates the employment of condition responsive control means (FIG. 2) to control a compressor motor 28 and valves 21, 37 and 39 in response to pressure switches 38 and 40 which communicate with receiver 16. The tank 33 located between valves 37 and 39 contains a non-condensable gas.
U.S. Pat. No. 3,238,737 to Schrader et al discloses (FIG. 2) a check valve 26 which releases refrigerant from liquid line 13A to a tank 17 (column 4, lines 27 to 53).
U.S. Pat. No. 1,815,962 to Andrews discloses a pressurized refrigerant container 40 to charge the refrigerant system. The patent also discloses opening valve 38 to allow the compressor 20 to pump reserve from the evaporator into the receiver.
U.S. Pat. No. 3,400,552 to Johnson et al discloses an electrically controlled refrigerant charging device employing a charge bottle 30. In the event of an overcharge condition, refrigerant is released via bleed valve 33 (column 4, lines 9 to 13).
U.S. Pat. No. 3,903,709 to Anderson et al discloses a refrigerant charging apparatus which automatically delivers incremental quantities of refrigerant from container 12 into the system until a proper level of charge is achieved.
However, none of these references disclose shutting down the compressor and collecting refrigerant which would be released to the atmosphere if it were not collected during a high pressure system failure.
U.S. Pat. Nos. 5,359,863 and 5,361,592 to Lewis disclose method and apparatus for preventing the release of refrigerant to the atmosphere during a high pressure system failure. A tank 34 acts as a receiver for refrigerant from safety relief valve 42 in the event the pressure in the system exceeds the safety relief valve set point. When the refrigerant pressure in receiver tank 34 increases, pressure switch 50 is activated, denying electric current to compressor 5.
U.S. Pat. No. 5,259,204 to McKeown discloses a refrigerant release prevention system adaptable for use with refrigerated containers for shipping food. Recovery tank 20 is connected to the outlet of an existing pressure relief valve 14 or to the outlet of secondary diverter valve 24A. When a system overpressure occurs, pressure switch 32 opens solenoid valve 28 to allow refrigerant to flow to the suction side of the compressor 30.
U.S. Pat. No. 5,408,840 to Talley discloses a refrigerant release prevention system designed for use on automobile air conditioning systems. Recovery tank 20 is connected to the outlet of an existing pressure relief valve via a check valve 32. When a system overpressure occurs, pressure switch 24 disables compressor clutch 80. Recovery tank 20 is equipped with a schrader valve 26 to facilitate removal of the recovered refrigerant at a repair facility (column 4, lines 46 to 48).
U.S. Pat. No. 5,319,945 to Bartlett discloses a system for non-atmospheric venting of refrigerant when evaporator 22 has an overpressure condition. Storage tank 36 is connected via a closed loop, pipes 54 and 56, to the evaporator. When a system overpressure occurs at a pressure less than the relief valve 26 setting, pressure switch 32 sends a signal to controller 34 which in turn shuts down refrigeration system 10. The stored refrigerant can be returned to the system after maintenance is performed.
In refrigeration systems, such as rack systems for frozen or refrigerated foods, which contain a plurality of compressors, it may not be necessary to shut down all of the compressors to prevent the release of refrigerant to the atmosphere. Multiple compressor systems which provide refrigerant to different zones or sections of a unit or space to be cooled may, for example, develop a high pressure problem which affects only one or a few zones or compressors. Accordingly, it may not be necessary to halt the supply of refrigerant and cooling to all zones or sections.
The present invention provides a refrigerant recovery system for multi-compressor refrigeration systems, such as a rack system for foods, which shuts down selected compressors to maintain limited system operation in the event of a system overpressure which causes the safety or relief valve to open and discharge refrigerant. Thus, release of refrigerant to the atmosphere can be avoided while providing cooling or refrigeration to selected or more critical zones requiring cooling. In embodiments of the invention the selected compressors are automatically restarted after a predetermined period of time while feeding the contained refrigerant back into the system. The invention also provides for shutting down the entire multi-compressor system when the system overpressure exceeds the relief valve setpoint by a substantial amount.
The present invention provides a method and apparatus for delivering refrigerant from the high pressure side of a multi-compressor refrigerant system to an evacuated sealed receiver and denying operating current to at least one selected compressor to prevent its or their operation when the high pressure safety valve opens so as to contain refrigerant which would otherwise be discharged into the atmosphere. However, while the one or more compressors are shut down, operating current is continued to be supplied to at least one selected compressor of the multiple compressor system. Thus, operation of the system may be continued when the high pressure safety valve opens while containing refrigerant which would otherwise be discharged into the atmosphere.